The heat waves in the center and west of Argentina

This work aims to: identify the heat waves that happen in the center and west of Argentina, to establish their climatology, to indentify the previous synoptic and dynamic conditions and the associated cloud structures. Once this is achieved the idea is to desing an objetive model to forecast the event that will allow not only to forecast an increase of the river flows in the Cordillera, but also to warn the agricultural producers of the phenomenon occurrence.

The daily minimum temperatures from the main meteorological stations located in the studied region were analyzed between October and March, during the 1989-99 period. Taking as a threshold the monthly minimum mean there appear non-real heat waves, and when considering the monthly maximum minimum mean temperature some waves are left unrecorded. So, for each locality it was obtained the optimum threshold of minimum mean temperature that indentifies the heat wave, and the minimum amount of consecutive occurrence days to define it.

There is a general trend for the heat waves to occur when in the middle and high layers of the atmosphere there is a persistent ridge or cutt-off high at 700, 500 and/or 300 hPa levels.

The satellite images preceding an extense and intense heat wave, show middle and high cloudiness, with a marked anticyclonic curvature, reaching from the Pacific Ocean to the east, going through the Cordillera de Los Andes, between 20° y 40°S latitude.

The behavior of the main cordilleran river flows was analyzed, quantifying the response time for snowmelt, accelerated by these meteorological conditions. The conclusion is that, besides the necessity for an objetive predictive model of the phenomenon as a whole, it is also necessary to adjust it for each particular zone.